[SYCL] VS2026 fix needs guard in complex (#22994)

test added

Author: cperkinsintel

sycl/include/sycl/ext/oneapi/experimental/complex/detail/common.hpp

@@ -49,8 +49,14 @@ struct is_gencomplex
 /// DEFINES
 ////////////////////////////////////////////////////////////////////////////////
 
+#if defined(_MSC_VER) && !defined(__clang__)
+// cl.exe does not understand GCC-style __attribute__((...)); it is only a
+// visibility/always-inline hint, so fall back to __forceinline for parity.
+#define _SYCL_EXT_CPLX_INLINE_VISIBILITY __forceinline
+#else
 #define _SYCL_EXT_CPLX_INLINE_VISIBILITY                                       \
   inline __attribute__((__visibility__("hidden"), __always_inline__))
+#endif
 
 } // namespace experimental
 } // namespace oneapi

sycl/test/extensions/complex/complex_host_compile_win.cpp

@@ -0,0 +1,29 @@
+// Regression test for CMPLRLLVM-77544. The SYCL complex experimental
+// extension's inline-visibility macro previously expanded to an unguarded
+// __attribute__((visibility(...), always_inline)), which cl.exe cannot parse.
+// That surfaced when icx/clang++ drives cl.exe as the SYCL host compiler
+// (e.g. torch-xpu-ops builds on Windows). The header now guards the macro
+// with _MSC_VER; this test ensures the partial specialization of complex<T>
+// keeps parsing under MSVC host compilation.
+
+// RUN: %clangxx -fsycl -fsycl-host-compiler=cl -fsycl-host-compiler-options='/std:c++20 /MD /EHsc /permissive- /DSYCL_DISABLE_FSYCL_SYCLHPP_WARNING' %s -c -o %t.o
+// REQUIRES: windows
+
+#define SYCL_EXT_ONEAPI_COMPLEX
+#include <sycl/ext/oneapi/experimental/complex/complex.hpp>
+#include <sycl/sycl.hpp>
+
+namespace syclex = sycl::ext::oneapi::experimental;
+
+// Force instantiation of the complex<T, enable_if<is_genfloat<T>>> partial
+// specialization for each supported floating-point type. Prior to the fix,
+// simply parsing the class body under cl.exe hit C2059 on the first member
+// decorated with _SYCL_EXT_CPLX_INLINE_VISIBILITY.
+void force_instantiate() {
+  syclex::complex<float> zf(1.0f, 2.0f);
+  syclex::complex<double> zd(1.0, 2.0);
+  syclex::complex<sycl::half> zh(sycl::half{1.0f}, sycl::half{2.0f});
+  (void)syclex::exp(zf).real();
+  (void)syclex::exp(zd).real();
+  (void)syclex::exp(zh).real();
+}